1. Field of the Invention
The present invention relates to a reciprocating compressor, and more particularly to, an apparatus and a method for controlling an operation of a reciprocating compressor.
2. Description of the Prior Art
In general, a reciprocating compressor compresses a refrigerant gas in a cylinder by linearly reciprocating a piston of the reciprocating compressor in the cylinder. The reciprocating compressor is classified into a rotary type reciprocating compressor and a linear type reciprocating compressor according to a method for driving a piston.
In the rotary type reciprocating compressor, a rotary motion of a rotary motor is transformed into a linear reciprocating motion of a piston by coupling a crank shaft to the rotary motor and coupling the piston to the crank shaft. In the linear type reciprocating compressor, a piston is coupled directly to a mover of a linear motor, for linearly reciprocating on the basis of a linear reciprocating motion of the mover.
Differently from the rotary type reciprocating compressor, the linear type reciprocating compressor does not have a crank shaft for transforming a rotary motion into a linear reciprocating motion, and thus reduces a friction loss. Therefore, the linear type reciprocating compressor shows higher operational efficiency than the rotary type reciprocating compressor.
The linear type reciprocating compressor (hereinafter, referred to as ‘compressor’) controls a stroke by controlling a voltage applied to a linear motor (hereinafter, referred to as ‘motor’) of the compressor according to a stroke reference value. Thus, a compression ratio of the compressor can be adjusted.
A conventional apparatus for controlling an operation of a compressor will now be explained with reference to FIG. 1.
FIG. 1 is a block diagram illustrating the conventional apparatus for controlling the operation of the compressor.
Referring to FIG. 1, the conventional apparatus for controlling the operation of the compressor includes: a voltage detection unit 140 for detecting a voltage applied to a motor; a current detection unit 150 for detecting a current applied to the motor; a stroke operator 160 for operating a stroke on the basis of the detected current value, the detected voltage value and parameters of the motor; a comparator 110 for comparing the operated stroke value with a stroke reference value, and outputting a difference value according to the comparison result; and a controller 120 for adjusting a compression ratio of the compressor 130 by controlling the stroke of the compressor 130 by controlling the voltage applied to the motor on the basis of the difference value.
The operation of the conventional apparatus for controlling the operation of the compressor will now be explained with reference to FIG. 2.
FIG. 2 is a flowchart showing sequential steps of the conventional method for controlling the operation of the compressor.
As depicted in FIG. 2, the conventional method for controlling the operation of the compressor includes the steps of: detecting the voltage applied to the motor (S201); detecting the current applied to the motor (S202); operating the stroke on the basis of the detected current value, the detected voltage value and the parameters of the motor (S203); comparing the operated stroke value with the stroke reference value, and outputting the comparison result (S204); and controlling the stroke of the compressor by controlling the voltage applied to the motor according to the comparison result (S205 and S206).
The conventional method for controlling the operation of the compressor will now be described in more detail.
The voltage detection unit 140 detects the voltage applied to the motor, and outputs the detected voltage value to the stroke operator 160 (S201).
The current detection unit 150 detects the current applied to the motor, and outputs the detected current value to the stroke operator 160 (S202).
The stroke operator 160 operates the stroke X by following formula 1 on the basis of the inputted current value, the inputted voltage value and the parameters of the motor (motor constant, resistance and inductance), and outputs the operation result to the comparator 110 (S203).
                    X        =                              1            α                    ⁢                      ∫                                          (                                                      V                    M                                    -                  Ri                  -                                      L                    ⁢                                          i                      .                                                                      )                            ⁢                              ⅆ                t                                                                        <                  Formula          ⁢                                          ⁢          1                >            
Here, α represents the motor constant, VM represents the voltage value detected in the motor, i represents the current value detected in the motor, R represents the resistance value of the motor, and L represents the inductance value of the motor.
The comparator 110 compares the inputted stroke value with the stroke reference value, and outputs the comparison result to the controller 120 (S204).
The controller 120 controls the voltage applied to the motor according to the inputted comparison result. That is, when the operated stroke value is smaller than the stroke reference value, the controller 120 increases the voltage applied to the motor (S205), and when the operated stroke value is larger than the stroke reference value, the controller 120 decreases the voltage applied to the motor (S206), thereby controlling the stroke of the compressor.
However, when the piston of the compressor reciprocates in the cylinder, mechanical oscillations are generated in the compressor. Here, the compressor has a unique mechanical resonance frequency.
On the other hand, operational efficiency of the compressor is changed according to an operating frequency. The relation between the operating frequency of the compressor and the operational efficiency of the compressor will now be explained with reference to FIG. 3.
FIG. 3 is a graph showing the operational efficiency of the conventional compressor.
As shown in FIG. 3, when a current operating frequency of the compressor is identical to a mechanical resonance frequency of the compressor, the compressor shows the highest operational efficiency.
However, when mechanical oscillations are generated in the compressor, even if the mechanical resonance frequency of the compressor is varied according to a load variation of the compressor, the compressor is operated with a constant operating frequency, which results in low operational efficiency.